6 6 D O C U M E N T 8 1 M A R C H 1 9 2 1 If (negative per Wirtinger), then , . Weyl’s invariant is correct.[4] I wanted to work on a few problems of rel[ativity] th[eory]. Would you be so kind and grant me some of your time? I am mainly thinking of the questions: If , and is regular and throughout finitude, is the manifold then necessarily Euclidean? I believe a paper by Lipschitz may be applicable to this question.[5] Another question: whether there is such a thing as a closed geodesic worldline.[6] I plan to write a book about the th. of rel. Also scientifically elaborating the mathematical aspect. It would be good if I could take my Habilitation degree here (until Palestine).[7] Would you provide me with assistance? Prof. von Mises is a magnificent person and one could talk about it with him.[8] With cordial regards, yours, J. Grommer. Besides, it does not seem right to me to confine oneself only to the second deriva- tives, if only the ratios of the ’s play a part. The additional condition could also contain higher derivatives. 81. To Alfred Kerr[1] [Berlin,] 7 March 1921 Dear Mr. Kerr, I hope your wife[2] is feeling well and your child[3] is in nondenominational bliss.[4] You had barely left when I received a letter from a rabbi who was supposed to sway me with cunning words into entering the religious community;[5] but Jeho- vah will stand by his disloyal son, that he stay firm.[6] – I thank you cordially for sending the books,[7] which I already relished dipping into. I am reminded of a Riklm 1 2 -- - xk xm 2 gil … + = Riklm g = Riklm 1 2 -- - gil mk gim kl – gkm il gkl im – + 3 4 ------(gil k m gim k l – – + + = gkm i l gkl i m ) 1 4 ------ gilgkm gimgkl – + – + Rkm g Rkm km -------- 3 2 2 -------- - k m – gkm 2 -------- g . + – + = R g R --- 3 2 ----- il gil 3 2 3 -------- - m m – + = Rik 0 = gik g 0 = gik